The present invention relates to a magnetoresistive head for use in a magnetic disc drive, and more particularly, to a method of forming a tunneling magnetoresistive (TMR) head.
A transducing head of a magnetic data storage and retrieval system typically includes a magnetoresistive (MR) reader portion for retrieving magnetic data stored on a magnetic medium. The reader is typically formed of several layers including an MR sensor positioned between two shield layers. The MR sensor may be any one of a plurality of MR-type sensors, including anisotropic magnetoresistive (AMR), giant magnetoresistive (GMR), tunneling giant magnetoresistive (TMR), spin valve, and spin tunneling sensors. When the transducing head is placed near a magnetic medium, a resistance of the MR sensor fluctuates in response to a magnetic field emanating from within transitions in the magnetic medium. By providing a sense current through the MR sensor, the resistance of the sensor can be measured and used by external circuitry to decipher the information stored on the magnetic medium.
TMR heads have proved to be especially attractive for high areal density applications due to their large signal output and reduced shield-to-shield spacing. TMR heads typically include a multi-layered portion called a TMR stack. The TMR stack includes a tunnel barrier layer positioned between two ferromagnetic layers. The tunnel barrier is a very thin electrically insulating layer, such as aluminum oxide (Al2O3), while the two ferromagnetic layers are typically formed of an electrically conductive ferromagnetic material. On one side of the tunnel barrier, the magnetization direction of the ferromagnetic layer is fixed and provides a reference direction for the TMR head. However, the magnetization direction of the ferromagnetic layer formed on the other side of the tunnel barrier rotates freely in response to an external magnetic field from the magnetic medium.
A sense current is supplied through the ferromagnetic layers and the tunnel barrier and flows perpendicular to the plane of the layers. While the tunnel barrier is an electrically insulating layer, electrons from the sense current can tunnel through the tunnel barrier. As the magnetization of the freely rotating ferromagnetic layer rotates in response to the external magnetic field from the magnetic medium, the resistance of the tunnel barrier changes. This resistance is related to the difference between the magnetization directions of the two ferromagnetic layers. By measuring the change in resistance (for example, by measuring the current flow) the TMR head can read the magnetic bits stored on the magnetic medium.
After the formation of the TMR stack, an air bearing surface is formed normal to the layers of the TMR stack. This is typically accomplished by lapping the TMR stack until the appropriate stripe height has been defined. Stripe height is defined as the height of the TMR stack from the air bearing surface to a back edge of the TMR stack, opposite the air bearing surface. This mechanical lapping process results in the formation of a layer of smearing and debris. It has been found that this layer of smearing and debris is detrimental to the sensitivity of the TMR head because the layer forms an low resistance path between the two ferromagnetic layers allowing electrons to bypass the tunnel barrier. In addition to the problems caused by the smearing and debris layer, the lapping process itself causes a degradation in the insulating properties of the tunnel barrier adjacent to the air bearing surface.
Various methods have been used to remove the smearing and debris layer from the TMR stack to improve the sensitivity of the TMR head. One such method is to use an ion beam etch to etch away the smearing and debris layer by bombarding the air bearing surface with energetic ions, such as argon ions. While the ion beam etch does remove the smearing and debris layer from the air bearing surface, it also results in a damaged layer on the air bearing surface of the TMR stack. The damaged layer, caused by the ion beam etch, includes various types of damage including vacancies, knock-ins, knock-outs, implanted argon, etc.